1. Field of the Invention
The present invention relates to a method for abutting and fusion splicing the splicing ends of optical fibers and an apparatus used in the method.
2. Description of the Background Art
When splicing ends of two optical fibers that are to be spliced to each other are melted, melting is usually brought about after aligning so that the respective core positions of the two optical fibers correspond. Alignment that is carried out in order to align the core positions is referred to in this specification as “core alignment”. When the core center and the fiber center do not correspond (when the core is decenterd), splicing will be performed in a state in which the positions of the two fibers are offset (condition in which the shapes of the fibers are offset) even though the positions of the two optical fiber cores are aligned to each other. In this case, the two optical fibers move so that the offset in the shapes is minimized due to the self-alignment effect (effect whereby offset at the external surface of the fibers is minimized due to surface tension of the optical fibers that are in a heated and melted state), which causes offset in the core positions (core offset) that had been in core alignment, and splicing loss thus increases.
Various proposals have been made with the aim of reducing core offset. Japanese Patent Application Publication No. S60-195505, for example, discloses reducing the heating power (discharge time, discharge current) used for melting when the core decentering is significant to prevent large core offset, and increasing heating power when core decentering is small. Japanese Patent Application Publication No. S60-111205 discloses estimating the amount of relative change in the positions of the two fibers due to the self-alignment effect (self-alignment value) that occurs when the optical fibers are fusion spliced, and offsetting the optical fibers prior to heating and melting so as to compensate for the self-alignment value.
When optical fibers are fusion spliced by discharge heating, a test discharge is usually carried out prior to fusion splicing in order to determine the appropriate heating level for melting the optical fibers. However, after performing the test discharge one time, subsequent test discharges are often omitted. Optical fibers tend to melt more by heat when additives such as fluorine are added in the cladding material and, for this reason, the self-alignment value of optical fibers is not uniform and depends on the type of optical fiber. In addition, due to the surrounding environment such as the temperature of the surroundings or wind present during the fusion splicing, it is not always the case that there is a constant relationship between the heating power and the melted state of the optical fiber.
In addition, there are many cases where a worker does not know the type of optical fibers to be spliced or whether there is core decentering. Consequently, as the number of types of optical fibers used increases, which is recently the case, it becomes difficult to set the intentional offset that will compensate for the self-alignment value.